This invention concerns food packaging especially fish, meat and meat products where the colour and bacterial count of the retailed product is important.
The problem is manageable for retail markets in the same area as the supply of carcasses because the product can be offered for sale shortly after the carcass is butchered and the cuts packaged on plastic trays covered with film. But the problem is more difficult for meat packers where the product remains chilled but in transit for some days. During this period the packer usually relies on one of two techniques; vacuum packing where the meat is placed in a barrier pouch, the pouch atmosphere is evacuated in a chamber so that the pouch shrinks around the meat. Alternatively in gas flushing the meat is placed in a barrier pouch, then the pouch is evacuated on a "schnorkel" machine and carbon dioxide is inserted.
These methods are used against spoilage bacteria and to ensure retention of the acceptable colour. Even with this precaution some discoloration of the colour of the meat is possible. If this problem were removable then radical changes in the preparation of meat would be possible. Consumers and supermarkets are typically situated in cities perhaps a long distance from the rural area in which the stock are raised and fattened, for example, Montana.
This geographical arrangement means that the retail packing is carried out in the cities along with the disposal of waste which the preparation of primals generates. This practice reduces to a minimum the time taken to present the meat for sale thereby showing good colour. If the product could be transported with no loss of colour or acceptable loss of colour then it would be possible for the retail packing to be done closer to the source of the stock, namely in rural areas.
Our work has shown that the discolouration experienced by meat packers using plastic bags and carbon dioxide arises from the use of foamed polystyrene trays because the occluded air in the trays equilibrates with the carbon dioxide in the pouch and becomes available to the surface of the meat. In the instances where nonfoamed plastic trays less than 1 mm thick are used, no gas release is expected but these are more expensive and less familiar to the consumer than thicker foamed trays. Accordingly meat packers wish to retain the use of trays which are already familiar to those in the industry.
In this specification "containers" means plastic trays commonly used in the food industry which are covered with transparent film; boxes made of expanded plastic pellets and foamed plastic boxes of the type used to transport refrigerated fish and meat.
"Packaging gas" means a gas or gas mixture used in the food industry which is selected for inertness to food and for suppression of growth in food spoilage organisms. These are commonly carbon dioxide and nitrogen.